Cellulosic fibrous structures, such as paper, are well known in the art. Frequently, it is desirable to have regions of different basis weights within the same cellulosic fibrous product. The two regions serve different purposes. The regions of higher basis weight impart tensile strength to the fibrous structure. The regions of lower basis weight may be utilized for economizing raw materials, particularly the fibers used in the papermaking process and to impart absorbency to the fibrous structure. In a degenerate case, the low basis weight regions may represent apertures or holes in the fibrous structure. However, it is not necessary that the low basis weight regions be apertured.
The properties of absorbency and strength, and further the property of softness, become important when the fibrous structure is used for its intended purpose. Particularly, the fibrous structure described herein may be used for facial tissues, toilet tissue, paper towels, bibs, and napkins, each of which is in frequent use today. If these products are to perform their intended tasks and find wide acceptance, the fibrous structure must exhibit and maximize the physical properties discussed above. Wet and Dry Tensile strengths are measures of the ability of a fibrous structure to retain its physical integrity during use. Absorbency is the property of the fibrous structure which allows it to retain contacted fluids. Both the absolute quantity of fluid and the rate at which the fibrous structure will absorb such fluid must be considered when evaluating one of the aforementioned consumer products. Further, such paper products have been used in disposable absorbent articles such as sanitary napkins and diapers.
Attempts have been made in the art to provide paper having two different basis weights, or to otherwise rearrange fibers. Examples include U.S. Pat. No. 795,719 issued Jul. 25, 1905 to Motz; U.S. Pat. No. 3,025,585 issued Mar. 20, 1962 to Griswold; U.S. Pat. No. 3,034,180 issued May 15, 1962 to Greiner et al; U.S. Pat. No. 3,159,530 issued Dec. 1, 1964 to Heller et al; U.S. Pat. No. 3,549,742 issued Dec. 22, 1970 to Benz; and U.S. Pat. No. 3,322,617 issued May 30, 1967 to Osborne.
Separately, there is a desire to provide tissue products having both bulk and flexibility, such as with through air drying (TAD). Improved bulk and flexibility may be provided through bilaterally staggered compressed and uncompressed zones, as shown in U.S. Pat. No. 4,191,609 issued Mar. 4, 1980 to Trokhan, which patent is incorporated herein by reference.
Several attempts to provide an improved foraminous member for making such cellulosic fibrous structures are known, one of the most significant being illustrated in U.S. Pat. No. 4,514,345 issued Apr. 30, 1985 to Johnson et al., which patent is incorporated herein by reference. Johnson et al. teaches hexagonal elements attached to the framework in a batch liquid coating process.
Another approach to making tissue products more consumer preferred is to dry the paper structure to impart greater bulk, tensile strength, and burst strength to the tissue products. Examples of paper structures made in this manner are illustrated in U.S. Pat. No. 4,637,859 issued Jan. 20, 1987 to Trokhan, which patent is incorporated herein by reference. U.S. Pat. No. 4,637,859 shows discrete dome shaped protuberances dispersed throughout a continuous network, and is incorporated herein by reference. The continuous network can provide strength, while the relatively thicker domes can provide softness and absorbency.
One disadvantage of the web disclosed in U.S. Pat. No. 4,637,859, is that drying such a web can be relatively energy intensive and expensive, and typically involves the use of through air drying equipment. In addition, the papermaking method disclosed in U.S. Pat. No. 4,637,859 can be limited with respect to the speed at which the web can be finally dried on the Yankee dryer drum. This limitation is thought to be due, at least in part, to the pattern imparted to the web prior to transfer of the web to the Yankee drum. In particular, the discrete domes described in U.S. Pat. No. 4,637,859 may not be dried as efficiently on the Yankee surface as is the continuous network described in U.S. Pat. No. 4,637,859. Accordingly, for a given consistency level and basis weight, the speed at which the Yankee drum can be operated is limited.
Conventional tissue paper made by pressing a web with one or more press felts in a press nip can be made at relatively high speeds. The conventionally pressed paper, once dried, can then be embossed to pattern the web, and to increase the macro-caliper of the web. For example, embossed patterns formed in tissue paper products after the tissue paper products have been dried are common.
However, embossing processes typically impart a particular aesthetic appearance to the paper structure at the expense of other properties of the structure. In particular, embossing a dried paper web disrupts bonds between fibers in the cellulosic structure. This disruption occurs because the bonds are formed and set upon drying of the embryonic fibrous slurry. After drying the paper structure, moving fibers normal to the plane of the paper structure by embossing breaks fiber to fiber bonds. Breaking bonds results in reduced tensile strength of the dried paper web. In addition, embossing is typically done after creping of the dried paper web from the drying drum. Embossing after creping can disrupt the creping pattern imparted to the web. For instance, embossing can eliminate the creping pattern in some portions of the web by compacting or stretching the creping pattern. Such a result is undesirable because the creping pattern improves the softness and flexibility of the dried web.
Accordingly, one object of the present invention is to provide a paper and method for making a multi-region paper web wherein the web has a predetermined pattern of relatively high and relatively low density regions, yet can be dried with relatively lower energy and expense.
Another object of the present invention is to provide a method for making a multi-region paper having at least two, and preferably at least three different basis weights.
Another object of the present invention is to provide a non-through air dried paper web having different basis weights and different densities.
Another object of the present invention is to provide a paper web having a visually distinct pattern provided by a combination and/or inteference of two different repeating, nonrandom patterns.